Remove extra curly braces

Question

In this MWE, I demonstrate my problem:

\documentclass{article}
\usepackage{seqsplit}
\newcommand{\dosomething}[1]{\uppercase{#1}}
\newcommand{\dosomethingelse}[1]{\seqsplit{#1}}
\begin{document}
    \dosomething{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}

    % works with extra {...}
    \dosomething{{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}}

    \dosomethingelse{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}

    % does not work with extra {...}
    \dosomethingelse{{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}}
\end{document}

Some commands work with extra curly braces, some don't. Why is that, and how can I make them work by preprocessing my arguments when they do have extra curly braces?

Answer 1

If the argument is not empty and starting spaces can be removed, then the following trick helps:

\makeatletter
\newcommand{\dosomethingelse}[1]{%
  \expandafter\seqsplit\expandafter{\@firstofone#1}%
}
\makeatother

\@firstofone is defined in the LaTeX kernel as:

\long\def\@firstofone#1{#1}

It grabs the first token as argument and outputs it again, thus it does "nothing". But if the argument is not a single token, but a token group in braces, then one level of braces are removed.

Answer 2

It mostly depend on what command you're dealing with.

If you have \textit{{xyz}}, the additional braces just add a level of grouping; for \seqsplit it's a completely different ballgame, because this command scans its argument one item at a time and a braced group is a single item.

This is described in the manual of seqsplit, in section 2.3:

2.3 Grouping and Commands

The command \seqsplit does not insert breakpoints between the letters inside braces {...}.

[...(omitted example)...]

The braces around {kahg} prevented a splitting of this group. This effect can be used for typesetting special substrings inside sequences.

Braces have a very important syntactical meaning and should not be used in a casual way.